A storage system is a computer that provides storage service relating to the organization of information on writable persistent storage devices, such as memories, tapes or disks. The storage system is commonly deployed within a storage area network (SAN) or a network attached storage (NAS) environment. When used within a NAS environment, the storage system may be embodied as a file server including an operating system that implements a file system to logically organize the information as a hierarchical structure of directories and files on, e.g. the disks. Each “on-disk” file may be implemented as a set of data structures, e.g., disk blocks, configured to store information, such as the actual data for the file. A directory, on the other hand, may be implemented as a specially formatted file in which information about other files and directories are stored.
The file server, or filer, may be further configured to operate according to a client/server model of information delivery to thereby allow many client systems (clients) to access shared resources, such as files, stored on the filer. Sharing of files is a hallmark of a NAS system, which is enabled because of its semantic level of access to files and file systems. Storage of information on a NAS system is typically deployed over a computer network comprising a geographically distributed collection of interconnected communication links, such as Ethernet, that allow clients to remotely access the information (files) on the filer. The clients typically communicate with the filer by exchanging discrete frames or packets of data according to pre-defined protocols, such as the Transmission Control Protocol/Internet Protocol (TCP/IP).
In the client/server model, the client may comprise an application executing on a computer that “connects” to the filer over a computer network, such as a point-to-point link, shared local area network, wide area network or virtual private network implemented over a public network, such as the Internet. NAS systems generally utilize file-based access protocols; therefore, each client may request the services of the filer by issuing file system protocol messages (in the form of packets) to the file system over the network identifying one or more files to be accessed without regard to specific locations, e.g., blocks, in which the data are stored on disk. By supporting a plurality of file system protocols, such as the conventional Common Internet File System (CIFS), the Network File System (NFS) and the Direct Access File System (DAFS) protocols, the utility of the filer may be enhanced for networking clients.
A SAN is a high-speed network that enables establishment of direct connections between a storage system and its storage devices. The SAN may thus be viewed as an extension to a storage bus and, as such, an operating system of the storage system enables access to stored information using block-based access protocols over the “extended bus”. In this context, the extended bus is typically embodied as Fibre Channel (FC) or Ethernet media adapted to operate with block access protocols, such as Small Computer Systems Interface (SCSI) protocol encapsulation over FC or TCP/IP/Ethernet.
A SAN arrangement or deployment allows decoupling of storage from the storage system, such as an application server, and some level of information storage sharing at the application server level. There are, however, environments wherein a SAN is dedicated to a single server. In some SAN deployments, the information is organized in the form of databases, while in others a file-based organization is employed. Where the information is organized as files, the client requesting the information maintains file mappings and manages file semantics, while its requests (and server responses) address the information in terms of block addressing on disk using, e.g., a logical unit number (lun).
Some SAN arrangements utilize storage appliances that implement virtual disks (vdisks), which are encapsulated data containers stored within a file system. An example of such a storage appliance is further described in U.S. patent application Ser. No. 10/215,917, entitled MULTI-PROTOCOL STORAGE APPLIANCE THAT PROVIDES INTEGRATED SUPPORT FOR FILE AND BLOCK ACCESS PROTOCOLS, by Brian Pawlowski, et al., now published as U.S. Patent Publication No. 2004/0030668 A1 on Feb. 12, 2004, the contents of which are hereby incorporated by reference. Similarly, vdisks are further described in U.S. patent application Ser. No. 10/216,453, entitled STORAGE VIRTUALIZATION BY LAYERING VIRTUAL DISK OBJECTS ON A FILE SYSTEM, by Vijayan Rajan, et al., now issued as U.S. Pat. No. 7,107,385 on Sep. 12, 2006, the contents of which are hereby incorporated by reference.
In multi-protocol storage systems that utilize both block-based and file-protocols, typically the block-based protocol utilizes a high-speed transport mechanism, such as Fibre Channel (FC) or InfiniBand (IB). Conversely, file-based protocol connections often utilize, for example, the NFS protocol operating over TCP/IP. The file-based systems typically include additional network overhead due to the nature of the file-based protocols, e.g., NFS or User Datagram Protocol (UDP), involved. This additional network overhead, from, for example, file mapping and management of file semantics, significantly reduces the data throughput available over the file-based protocol network connection.
Clients typically desire the ease of use of a file-based protocol, especially the use of the file-based protocol namespace wherein the files are referenced through a conventional drive/volume/path/file name mechanism. In contrast, in a SAN or other block-based environment, data is accessed by reference to a set number of blocks spread among the disks storing the data for the data set, which imposes a greater administrative burden on a user for using SAN-based systems. However, a noted disadvantage of the use of the file-based protocols is the above-mentioned additional network overhead required for the use of such protocols. This additional network overhead makes the use of these file-based protocols impractical for certain high-performance and data-intensive transfer operations, such as database management systems (DBMS). Many users thus desire the ease of use of a file-based protocol namespace, while needing the high-speed data throughput available from a block-based protocol.
Thus, it is a object of the present invention to enable a client to transparently use a file-based protocol namespace while permitting the performance advantages of block-based protocol access to data stored on a storage system.